Diabetes is a general term for disorders in man having excessive urine excretion as in diabetes mellitus and diabetes insipidus. Diabetes mellitus is a metabolic disorder in which the ability to utilize glucose is more or less completely lost. About 2% of all people suffer from diabetes.
Since the introduction of insulin in the 1920's, continuos strides have been made to improve the treatment of diabetes mellitus. To help avoid extreme glycemia levels, diabetic patients often practice multiple injection therapy, whereby insulin is administered with each meal.
In the treatment of diabetes mellitus, many varieties of insulin preparations have been suggested and used, such as regular insulin, Semilente.RTM. insulin, isophane insulin, insulin zinc suspensions, protamine zinc insulin, and Ultralente.RTM. insulin. As diabetic patients are treated with insulin for several decades, there is a major need for safe and life quality improving insulin preparations. Some of the commercial available insulin preparations are characterized by a fast onset of action and other preparations have a relatively slow onset but show a more or less prolonged action. Fast acting insulin preparations are usually solutions of insulin, while retarded acting insulin preparations can be suspensions containing insulin in crystalline and/or amorphous form precipitated by addition of zinc salts alone or by addition of protamine or by a combination of both. In addition, some patients are using preparations having both a fast onset of action and a more prolonged action. Such a preparation may be an insulin solution wherein protamine insulin crystals are suspended. Some patients do themselves prepare the final preparation by mixing an insulin solution with a suspension preparation in the ratio desired by the patient in question.
Human insulin consists of two polypeptide chains, the so-called A and B chains which contain 21 and 30 amino acids, respectively. The A and B chains are interconnected by two cystine disulphide bridges. Insulin from most other species has a similar construction, but may not contain the same amino acids at the positions corresponding in the chains as in human insulin.
The development of the process known as genetic engineering has made it possible easily to prepare a great variety of insulin compounds being analogous to human insulin. In these insulin analogues, one or more of the amino acids have been substituted with other amino acids which can be coded for by the nucleotide sequences. As human insulin, as explained above, contains 51 amino acid residues, it is obvious that a large number of insulin analogues is possible and, in fact, a great variety of analogues with interesting properties have been prepared. In human insulin solutions with a concentration of interest for injection preparations, the insulin molecule is present in associated form as a hexamer (Brange et al. Diabetes Care 13, (1990), 923-954). After subcutaneous injection, it is believed that the rate of absorption by the blood stream is dependent of the size of the molecule, and it has been found that insulin analogues with amino acid substitutions which counteract or inhibit this hexamer formation have an unusual fast onset of action (Brange et al.: Ibid). This is of great therapeutic value for the diabetic patient.
Pharmaceutical preparations which are based on analogues of human insulin have e.g. been presented by Heinemann et al., Lutterman et al. and Wiefels et al. at the "Frontiers in Insulin Pharmacology" International Symposium in Hamburg, 1992.
Furthermore, U.S. Pat. No. 5,474,978 discloses a rapid acting parenteral formulation comprising a human insulin analogue hexamer complex consisting of six monomeric insulin analogues, zinc ions and at least three molecules of a phenolic derivative.
Normally, insulin preparations are administered by subcutaneous injection. What is important for the patient, is the action profile of the insulin preparation which is the action of insulin on the glucose metabolism as a function of the time from the injection. In this profile, inter alia, the time for the onset, the maximum value and the total duration of action are important. A variety of insulin preparations with different action profiles are desired and requested by the patients. One patient may, on the same day, use insulin preparations with very different action profiles. The action profile requested is, for example, depending on the time of the day and the amount and composition of any meal eaten by the patient.
Equally important for the patient is the chemical stability of the insulin preparations, especially due to the abundant use of pen-like injection devices such as devices which contain Penfill.RTM. cartridges, in which an insulin preparation is stored until the entire cartridge is empty. This may last for at least 1 to 2 weeks for devices containing 1.5-3.0 ml cartridges. During storage, covalent chemical changes in the insulin structure occur. This may lead to formation of molecules which are less active and potentially immunogenic such as deamidation products and higher molecular weight transformation products (dimers, polymers, etc.). A comprehensive study on the chemical stability of insulin is given in by Jens Brange in "Stability of Insulin", Kluwer Academic Publishers, 1994.
Acta Pharmaceutica Nordica 4(4), 1992, pp. 149-158 discloses insulin preparations in which the sodium chloride concentration has been varied in the range of 0 to 250 mM. However, the major part of the preparations, including all preparations which additionally comprises glycerol, contains a rather high amount of sodium chloride, i.e. 0.7% corresponding approximately to a concentration of 120 mM. It is stated in this document that whereas sodium chloride generally has a stabilizing effect on insulin preparations, glycerol and glucose lead to increased chemical deterioration.
Surprisingly, however, it has now been shown that insulin preparations of superior chemical stability can be obtained in the presence of glycerol and/or mannitol and rather low halogenide concentrations.